In 2024, the taste will become stronger In order to be neat and beautiful, people should often wash their clothes, bedding, daily tableware, and tea sets. This chemical process is very widespread in life. From simple soaps to complex detergent products, the progress of detergents represents the development of the chemical industry and the higher requirements of human beings for the quality of life. Be able to understand the washing principle of soap and other derivative products, and have a methodical analysis of the use method and the impact on the environment, which also has a good guiding role in the use of detergents in life. 
In order to be neat and beautiful, people should often wash clothes, bedding, daily tableware, and tea sets. This chemical process is very widespread in life. From simple soaps to complex detergent products, the progress of detergents represents the development of the chemical industry and the higher requirements of human beings for the quality of life. Be able to understand the washing principle of soap and other derivative products, and have a methodical analysis of the use method and the impact on the environment, which also has a good guiding role in the use of detergents in life.
1. The invention of soap
Soap predates detergent much earlier, and it is said that it was inadvertently made more than 3,000 years ago on Mount Santa Po, just outside the city of Rome. On this sacred mountain, when people burn offerings, the grease drips onto the ashes of the plants and trees to become the most primitive soap, which seeps into the surrounding clay. It was found that when they sat on the clay, it was easier to wash their clothes when they were stained with clay. People began to worship it as a sacred land, only to learn later that it was an unintentional harvest of labor.
In 70 AD, the Roman scholar Pliny described the process of making soap from goat fat and wood ash. There's another thing to add in the process--- sea salt. It causes the soap to float on top of the mixture, which is what we call salting out today. This account is probably the earliest description of the soap industry. Due to the low production at that time, it could only be used by the wealthy, and it was a luxury for the filthy.
In 1791, the French chemist Nicoles Caibrandz used sodium chloride aqueous solution to electrolyze sodium hydroxide, and since then, soap has become a common people's thing. However, not everyone knows what soap is.
From 1811 to 1823 after the study of soap products by Czevlull, it was satisfactorily explained what soap was and the chemical reaction that led to its manufacture.
Second, the manufacturing principle of soap
Fat and sodium hydroxide are boiled together and hydrolyzed into sodium and glycerol, which are processed and molded into soap. Soap is actually a salt of sodium, potassium, or triethanolamine [N(CH2CH2OH)3] of long-chain organic carboxylic acids. These salts of other carboxylic acids are also industrial soaps, but they do not have a decontamination or cleaning effect.
Put animal fat or vegetable oil and sodium hydroxide solution in a certain ratio in a saponification pot and stir to make it saponification reaction. After the reaction is completed, the resulting sodium salts of higher fatty acids, glycerol and water form a mixture; Then add salt fines to the pot, stir, and let it stand, so that the sodium of higher fatty acids is precipitated from the mixture and floats on the liquid surface, so as to separate from glycerol and salt water, this process is called salting out. The resulting soap contains 50 to 60 water and is paste-like. Continue to heat and dehydrate it, and when there is about 30 water left, it can be made into a solid, cake-like stick, and then air dry it until only 10 15 water remains, and then it can be cut into pieces. It can be further dried to a water content of only 5 10 when it can be made into powder.
The reaction equation is:
C17H35COO)3C3H5 3NaOH (solution) 3C17H35CoONA+C3H5(OH)3
The above reaction can explain the process by which the ancient Romans made soap. The animal fat used as a sacrifice contains triglycerides, and the hydrolysate of wood ash contains potassium hydroxide or sodium hydroxide, and when they are heated together, the fat is broken down to form small amounts of glycerol and soap.
3. Types of soap
Sodium salts of higher fatty acids are usually used the most, and are generally called hard soaps. Its potassium salt is called soft soap, and it is mostly used for shampooing and shaving. Its ammonium salt is often used to make alabaster.
According to the composition of the soap, from the fatty acid part, the soap made of fatty acids with high saturation is relatively hard; On the other hand, soaps made from fatty acids with greater unsaturation are softer. The main raw material of soap is grease with a high melting point.
In terms of the length of the carbon chain, generally speaking, the carbon chain of fatty acids is too short, and the solubility of the soap made in water is too large; If the carbon chain is too long, the solubility is too small. Therefore, only C10 C20 fatty acid potassium salt or sodium salt is suitable for soap, in fact, soap contains the most sodium salt of C16 C18 fatty acids.
Soap also usually contains a lot of water. After adding spices, dyes and other fillers to the finished product, various soaps are obtained.
The yellow laundry soap commonly used is generally mixed with rosin, which is added in the form of sodium salt, the purpose of which is to increase the solubility and foaminess of the soap, and it is also relatively cheap as a filler.
White laundry soap is added with sodium carbonate and water glass (up to 12%), and the composition of general laundry soap contains about 30% water. If the white laundry soap is dried and cut into thin slices, soap flakes are obtained, which are used to wash high-grade fabrics.
Add an appropriate amount of phenol and cresol mixture (antiseptic, sterilizing) or boric acid to the soap to obtain medicated soap.
Soap requires more advanced raw materials, for example, soap made by mixing butter or palm oil with coconut oil, crushing, drying to a water content of about 10 15, and then adding spices and dyes, pressing and molding.
Liquid potassium soap is often used as shampoo and other ingredients, and is usually made from coconut oil.
Fourth, the mechanism of soap decontamination
Soaps made from natural ingredients use four types of fats: butter, palm oil, coconut oil and olive oil.
In order for organic acids to have washing ability, they must contain a long chain of more than 9 carbons, and the washing ability increases with the growth of the carbon chain. However, soaps with molecules of more than 18 carbons are insoluble in water, even in hot water. Oleic acid (which contains exactly 18 carbons) is a very good detergent because its cis double chain is between the ninth and tenth carbon atoms, i.e. in the middle of the molecule.
In fact, most organic detergents are made into dipole molecules, which are long chains of 12 to 18 carbon atoms. One end contains a hydrophobic group (which repels water) and the other end contains a hydrophilic group (which attracts water).
Therefore, soap containing 18 carbon has better washing ability, while soap containing 12 carbon molecules has enhanced solubility in water. Soaps consisting of long-chain molecules containing more than 18 carbons are only used as fillers for scrubbing. This scrub needs to have the ability to remove contamination without being soluble.
In order to improve the washing performance of soap, it is necessary to understand the mechanism by which soap can remove stains. The process of decontamination is to remove dirt and oil with a thin film, which brings the dirt to the solution and emulsifies or removes it in suspension. In addition, as a detergent, it should be able to reduce the surface tension of the water interface, so that the washing liquid can penetrate into the small gaps of the fabric and speed up the process of fabric wetting.
For a substance to have the ability to decontaminate, it must first be able to reduce the surface tension of the solution. The surface tension of pure water is 272 dynes per centimeter. However, as an effective detergent, the surface tension must be reduced to 230 dynes per centimeter, and only a small amount of detergent is required to reduce the surface tension to this value.
A typical force acting on a water molecule causes molecules on the surface of the water to enter the solution--- which creates surface tension. When the molecules of soap are added to the water, it floats to the surface of the water because at the end of the organic matter (hydrophobic) it is repelled by the polar water molecules. Since the soap molecules are repelled by the water molecules on the surface of the water, a force is created against the mutual attraction of the water molecules, and as a result, the surface tension is reduced. When soapy water is added to the fabric fibers, the oil attached to the surface of the fabric gathers into small droplets and leaves the fabric surface. The end of the organic matter in the soap dissolves in the oil and leaves it away from the fabric fibers. At the same time, the water is constantly wriggling underneath, speeding up the speed at which the oil droplets leave. Polar groups in cotton fibers (e.g., hydroxy-OH in cellulose) attract water, causing it to diffuse (penetrate) throughout the fabric.
In general, the response to decontamination and descaling is generally similar. However, because the dirt can be electrically neutral, or positively charged or negatively charged. Therefore, some revisions to this simple theory are also necessary.
5. The principle of soap decontamination
The main principle lies in its molecular structure. Soap is a sodium salt of higher fatty acids, and its molecule can be divided into two parts: one part is a polar carboxyl group, which is easily soluble in water, is hydrophilic and oil-phobic, called hydrophilic group; The other part is a non-polar hydrocarbon group, which is insoluble in water and soluble in oil, and is lipophilic and hydrophobic, which is called a hydrophobic group. (Its molecules resemble tadpoles or matchsticks.) Its big "head" is a polar carboxyl group, which is easily soluble in water and is a hydrophilic and oil-repellent group. Its long "tail" is a non-polar hydroxyl group, which is miscible with organic matter and is a lipophilic and hydrophobic group) is chemically called the "similarity compatibility principle".
For example, when soap is dissolved in water, on the surface of the water, the hydrophilic carboxyl portion of the soap molecule tends to enter the water molecule, while the hydrophobic hydrocarbon portion is repelled from the water, forming a directional arrangement of soap molecules. The presence of this layer of higher fatty acid salts weakens the gravitational attraction between water molecules on the surface of the water, so soap can strongly reduce the surface tension of the water, and is therefore a surfactant.
When the concentration of soap in water is low, the soap molecules are in the form of single molecules, which are gathered on the surface of the water, i.e., the hydrophilic group enters the water, and the hydrophobic group is repelled outside the water.
When the concentration of soap in the water gradually increases, the soap molecules that accumulate on the surface of the water gradually increase and form a monolayer.
As the concentration of soap continues to increase, the hydrophobic hydrocarbon groups in the soap molecules inside the aqueous solution begin to gather together by van der Waals forces as the surface of the water is already occupied, while the hydrophilic carboxyl groups are wrapped around the outside to form colloidal-sized aggregate particles, called micelles. The micelles of soap are spherical in shape, and the lowest concentration at which micelles are formed is known as the critical micelle concentration.
Before and after the critical micelle concentration, the decontamination capacity has a great relationship with the concentration of the soap: below the critical micelle concentration, the decontamination capacity decreases sharply as the concentration of the soap decreases. When the critical micelle concentration is reached, the surface of the water is filled and the surface tension of the water is reduced to a minimum. Beyond the critical micelle concentration, the decontamination capacity can hardly change with the concentration of the soap. Increasing the concentration of soap in the water can only increase the number of micelles in the solution. The same goes for other detergents.
When washing clothes, when the oil stains or dirt on the clothes are coated with soap, the soap molecules will infiltrate into the gaps of the clothes, and the hydrophobic hydrocarbon part of the soap molecule will dissolve into the oil stain, and its lipophilic group will desperately enter the oil particles and combine with the oil stain, while the hydrophilic group will lie dead in the water, and the hydrophilic carboxyl part will stretch out in the water outside the oil stain, and the oil stain will be pulled down by the soap molecules. After the oil is drained, the oil is surrounded by soap molecules to form a stable emulsion. Because the "amphibious" structure of soap molecules also has an emulsifying effect, and becomes an oil-in-water emulsion similar to milk, soybean milk, and pesticide emulsions, so that the dirt is dispersed in the water and no longer returns to the clothes, in the washing process, the soap molecules surround the grease and dirt and decompose it into many small pieces, through mechanical friction, rubbing and water washing, the oil and other dirt will be separated from the attachment and dispersed into smaller emulsion droplets into the water, and leave with the water rinsing. This is the most important role of soap decontamination, which is the washing principle of soap
6. Defects in soap
Ever since the principles of soap stain removal were recognized, attempts have been made to improve their performance. Because soap has many drawbacks. Although soap has an excellent washing effect, it also has some drawbacks.
It dissolves well in cold water and dissolves well in hot water.
Soap should not be used in acidic water, in an acidic solution it does not play a good washing role, because it will decompose into insoluble acidic soap and fatty acid clumps in acidic solution.
Soap has a weakness one day, that is, it is afraid of hard water. Soap is not suitable for use in hard water, as it reacts with elements such as calcium, magnesium, aluminum, and iron in the water to form a precipitation of calcium salts of fatty acids (or magnesium stearate) that is insoluble in water (to form so-called metal soap), destroying its ability to decontaminate. This is the reason why ring-shaped dirt appears after basins and buckets are filled with soapy water, and a non-obvious film appears after the fabric is washed with soap. Not only is the soap wasted, but the decontamination ability is also greatly reduced. Soap is a good detergent in soft water. Unfortunately, the water we use in our daily lives, especially in rural areas, is often hard.
To make soap, a large amount of animal and vegetable oil is consumed, so in recent years, many substances with surface active effects have been synthesized according to the washing principle of soap. These substances are called synthetic surfactants, which are not only used for washing, but also have other uses.
Synthetic detergents such as laundry detergent are made from petroleum, sulfuric acid, and sodium dodecylbenzene sulfonate, which are typical amphibious molecules. Laundry detergent has a stronger stain removal ability than soap, and its adaptability is wider than that of soap. The sodium tripolyphosphate in the laundry detergent can form a water-soluble complex with calcium and magnesium ions in hard water, so it does not affect its decontamination effect.
In short, with the improvement of people's living standards, various new detergents continue to be put into the market. These products enrich our lives and bring us a neat, clean and comfortable environment. But at the same time, we must pay enough attention to the problem of water pollution caused by washing water, so as to prevent it from happening.